The newspaper spoke to a number of companies which claimed their employees had read people’s emails, including software firm Edison Software and eDateSource Inc, which used the data to tweak its algorithms.

As the owner of the email account is in charge of granting the application permission to read their messages, the practice does not breach Google’s user agreement, the company said.

It added that some developers had been denied access to Gmail as they failed to meet specific criteria outlined in Google’s verification process, including not asking for permissions the apps will not use.

Google’s developer policies state: “There should be no surprises for Google users: hidden features, services, or actions that are inconsistent with the marketed purpose of your application may lead Google to suspend your ability to access Google API Services.”

Gmail account holders can check the third-party applications linked to their account under the Security Check-up page.

“When a user connects through third party email applications, the application has access to all content because, technically, your connection to the email application is via the mail server where all emails are stored. So, it’s true that all third-party email applications have access to your Gmail accounts, if you connected them,” said Evgeny Chereshnev, chief executive of wearable firm Biolink.Tech.

“This type of access is going to going to continue, and people need to be aware that every time they connect to, or install, a third-party application on their mobile device, they are giving rights to those applications – often without even thinking about it. These applications gain access to users’ contacts, information about the user of the phone as well as things like GPS location, so this needs to be taken very seriously.”

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